Garnet powder, manufacturing method thereof, solid electrolyte sheet using hot press and manufacturing method thereof

ABSTRACT

The present disclosure relates to garnet powder, a manufacturing method thereof, a solid electrolyte sheet using a hot press, and a manufacturing method thereof. In particular, the present disclosure provides a method for manufacturing Li 7 La 3 Zr 2 O 12  (LLZ) garnet powder including preparing a mixture by first dry mixing Li 2 CO 3 , La 2 O 3 , ZrO 2 , and Al 2 O 3 . The mixture is first calcinated for 5 to 7 hours in a temperature range of 800 to 1000° C. The calcinated mixture is ground to a powder with an average particle size of 1 to 4 μm through dry grinding. A cubic-phased LLZ garnet powder is prepared by second calcinating the ground mixture for 10 to 30 hours in a temperature range of 1100 to 1300° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. § 119(a) the benefit of KoreanPatent Application No. 10-2014-0106858 filed on Aug. 18, 2014, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to garnet powder, a manufacturing methodthereof, a solid electrolyte sheet using a hot press and a manufacturingmethod thereof, and in particular, to garnet powder in which the garnetpowder is obtained in high yields compared to existing garnet pelletshaving a very small amount of LLZ (Li₇La₃Zr₂O₁₂) garnet powder, and asolid electrolyte sheet using this garnet powder has a pure cubic-phasedcrystal structure without impurities by using a hot press process, andis effective in improving ionic conductivity compared to existing solidelectrolytes, a manufacturing method of the garnet powder, a solidelectrolyte sheet using a hot press, and a manufacturing method of thesolid electrolyte sheet.

BACKGROUND

Secondary batteries are batteries that undergo repeated charging anddischarging by chemical energy and electric energy being interconvertedthrough the chemical reactions of oxidation and reduction. Secondarybatteries generally include four basic elements: an anode, a cathode, aseparator, and an electrolyte. Herein, the anode and the cathode arecollectively referred to as an electrode, and among the elements formingelectrode materials, a material causing the actual reaction is referredto as an active material.

Generally, lithium ion secondary batteries use a liquid electrolyte andan electrolyte including a liquid. However, liquid electrolytes havedisadvantages in that they are volatile, and therefore, may present anexplosion hazard. In addition, the liquid electrolytes have inferiorthermal stability.

Meanwhile, solid state batteries using a solid state electrolyte havelow danger of explosion, and also have excellent thermal stability. Inaddition, when a bi-polar plate is used, high operating voltage may beobtained by a series connection through electrode lamination, and inthis case, higher energy density may be obtained compared to the energydensity in a series connection mode of cells using a liquid electrolyte.

In order to prepare such an all solid state battery, a solid electrolytetransferring lithium ions is necessary. Solid electrolytes are largelydivided into an organic (polymer) electrolyte and an inorganicelectrolyte. The inorganic electrolyte is further divided into anoxide-type electrolyte and a sulfide-type electrolyte.

Of these, the oxide-type solid electrolyte is an oxygen-includingelectrolyte, such as a LiPON-type, a perovskite-type, a garnet-type anda glass ceramic-type. Oxide-type solid electrolytes have an ionicconductivity of 10⁻⁵ to 10⁻³ S/cm lower than sulfide-based electrolytes.The oxide-type solid electrolyte, however, has advantages in that theoxide-type solid electrolyte is stable with respect to moisture and thereactivity in the atmosphere due to oxygen is low, as compared to thesulfide-type solid electrolyte.

The oxide-based solid electrolyte has high grain boundary resistance,and therefore, an electrolyte membrane or pellets, in which neckingbetween the particles are formed from high temperature sintering, may beused, and there is a problem in that mass productivity is very low toform a large-area electrolyte membrane since high temperature sinteringis carried out at a temperature of 900 to 1400° C.

Particularly, a garnet-type solid electrolyte requires a long time of 6hours or longer at a high temperature of 1000 to 1200° C. in finalcalcination, and in order to prevent lithium volatilization, and tosecure phase changes and composition uniformity, pellet-covered garnetmay be used. However, there is a disadvantage in that the proportion ofgarnet secured using such pellets is usually less than 20% by weightwith respect to the total weight, which is a very small amount.

The US Patent Application Publication No. 2013-0344416 discloses solidoxide ceramics prepared by hot pressing pellets that are preparedincluding lithium carbonate, lanthanum hydroxide, zirconium oxide, andalumina; however, there is a disadvantage in that pellet-type LLZ withlow crystallizability is formed.

Accordingly, in order to secure a large amount of garnet powder, muchresearch has been conducted, including basic physical property studies,preparation of garnet sheet, preparation of a complex solid electrolyteof garnet and polymers, and studies on the materials capable of beingutilized in the manufacturing process of all solid state batteries.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

The present disclosure has been made in an effort to solve theabove-described problems associated with the prior art. The inventors ofthe present disclosure have found that garnet powder may have a purecubic-phased crystal structure with high crystallizability while beingproduced in a higher yield. By manufacturing a solid electrolyte sheetusing this garnet powder through a hot press process, the solidelectrolyte sheet may have improved ionic conductivity compared toexisting solid electrolytes. Accordingly, in an embodiment of thepresent disclosure a garnet powder having a cubic-phased crystalstructure is provided.

In another embodiment of the present disclosure a method formanufacturing the garnet powder in an improved yield compared toexisting garnet pellets is provided.

In another embodiment of the present disclosure a solid electrolytesheet including the garnet powder, which has improved ionicconductivity, is provided.

In another embodiment of the present disclosure a method formanufacturing the solid electrolyte sheet using a hot press is provided.

Another embodiment of the present disclosure provides LLZ (Li₇La₃Zr₂O₁₂)garnet powder having a cubic-phased crystal structure, wherein a molarratio of the Li:La:Zr atoms is 6.5 to 8.3 mol:3 mol:2 mol.

In another embodiment, the present disclosure provides a method formanufacturing LLZ (Li₇La₃Zr₂O₁₂) garnet powder including preparing amixture by first dry mixing Li₂CO₃, La₂O₃, ZrO₂, and Al₂O₃; and themixture is first calcinated for 5 to 7 hours in a temperature range of800 to 1000° C. The calcinated mixture is ground to a powder size of 1to 4 μm through dry grinding. A cubic-phase LLZ (Li₇La₃Zr₂O₁₂) garnetpowder is prepared by second calcinating the ground mixture for 10 to 30hours in a temperature range of 1100 to 1300° C.

In another embodiment, the present disclosure provides a solidelectrolyte sheet including the LLZ (Li₇La₃Zr₂O₁₂) garnet powder.

In a further embodiment, the present disclosure provides a method formanufacturing a solid electrolyte sheet using a hot press includingpreparing the LLZ (Li₇La₃Zr₂O₁₂) garnet powder; and manufacturing asolid electrolyte sheet by hot pressing the garnet powder for 30 minutesto 2 hours in a temperature range of 1050 to 1250° C. under an argonatmosphere.

Other aspects and embodiments of the invention are discussed infra.

LLZ (Li₇La₃Zr₂O₁₂) garnet powder according to the present disclosure isprepared through a two-step calcination processes as a powder itself. Asa result, the obtained garnet powder content is high compared toexisting garnet pellets having a very small amount of garnet powder, andthe prepared LLZ garnet powder has a cubic-phased crystal structure withhigh crystallizability.

In addition, a solid electrolyte sheet including the LLZ (Li₇La₃Zr₂O₁₂)garnet powder according to the present disclosure uses a hot pressprocess, therefore, a solid electrolyte sheet having a pure cubic-phasedcrystal structure may be manufactured without including impurities, andthe solid electrolyte sheet is effective in improving ionic conductivitycompared to existing solid electrolytes.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated in the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present disclosure.

FIG. 1 illustrates XRD measurement results of garnet powder manufacturedin Example 1 and Comparative Examples 1 to 3 of the present disclosure.

FIG. 2A is a Raman measurement result of garnet powder manufactured inExample 1 of the present disclosure.

FIG. 2B is a Raman measurement result of garnet powder manufactured inComparative Example 1 of the present disclosure.

FIG. 2C is a Raman measurement result of garnet powder manufactured inComparative Example 2 of the present disclosure.

FIG. 2D is a Raman measurement result of garnet powder manufactured inComparative Example 3 of the present disclosure.

FIG. 3 shows ICP measurement results of garnet powder manufactured inExample 1 and Comparative Examples 1 to 3 of the present disclosure.

FIG. 4 is an SEM picture of garnet powder manufactured in Example 1 ofthe present disclosure.

FIG. 5 is a graph showing density and ionic conductivity of solidelectrolyte sheets prepared in Example 2 and Comparative Examples 4 and5 of the present disclosure.

FIG. 6 is XRD measurement results of solid electrolyte sheets preparedin Examples 1 and 2 and Comparative Examples 4 and 5 of the presentdisclosure.

FIGS. 7A-7C are Raman measurement results of solid electrolyte sheetsprepared in Example 2 and Comparative Examples 4 and 5 of the presentdisclosure.

FIGS. 8A-8C are SEM pictures of solid electrolyte sheets prepared inExample 2 and Comparative Examples 4 and 5 of the present disclosure.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present disclosure asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present disclosure, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

The present disclosure provides LLZ (Li₇La₃Zr₂O₁₂) garnet powder havinga cubic-phased crystal structure in which the molar ratio of theLi:La:Zr atoms is 6.5 to 8.3:3:2.

The LLZ (Li₇La₃Zr₂O₁₂) garnet powder is divided into cubic-phased ortetragonal-phased, and herein, the cubic-phased is reported to haveexcellent ionic conductivity of 100 times or higher with thecubic-phased having ionic conductivity of approximately 10⁻⁴ S/cm andthe tetragonal-phased having ionic conductivity of approximately 10⁻⁶S/cm. Accordingly, synthesizing to have a cubic-phased crystal structureinstead of impurities, secondary-phased or tetragonal-phased isadvantageous in improving the physical properties.

In embodiments of the LLZ garnet powder, the molar ratio of the Li atomranges from 6.5 to 8.3 mol. When the molar ratio is less than 6.5 mol,garnet powder having a cubic-phased crystal structure is not produced,and when the molar ratio is greater than 8.3 mol, there is a problem inthat ionic conductivity rapidly decreases due to the presence ofimpurities. Generally, Li volatilization most actively occurs at atemperature of approximately 900° C. or higher, therefore, the Li atommay be used in greater than 10 mol %. In a certain embodiment, the molarratio of the Li:La:Zr atoms is preferably 7:3:2.

In certain embodiments, some of the Li of the LLZ garnet powder may besubstituted with Al. Herein, the Al stabilizes the cubic-phased crystalstructure and affects the density increase with a liquid phase sinteringeffect, and may improve the ionic conductivity of the powder.Consequently, some of the Li may be substituted with Al in thesynthesis.

The Al may be substituted in a range of 0.02 to 1.075 mol. The Al may bedoped in the form of Al₂O₃ at 0.1 to 5% by weight with respect to theLLZ. Specifically, when the Al₂O₃ is doped in less than 0.1% by weight,physical properties of a solid electrolyte may be degraded, and when indoped greater than 5% by weight, there is a problem in that impurities(Al₃Zr, Li₂ZrO₃) are produced with the cubic-phased powder. In a certainembodiment, the Al₂O₃ is doped at 3.69% by weight.

In addition, the present disclosure provides a method for manufacturingLLZ (Li₇La₃Zr₂O₁₂) garnet powder including preparing a mixture by firstdry mixing Li₂CO₃, La₂O₃, ZrO₂, and Al₂O₃. The mixture is firstcalcinated for 5 to 7 hours in a temperature range of 800 to 1000° C.The calcinated mixture is ground to a powder with an average particlesize of 1 to 4 μm through dry grinding. The cubic-phased LLZ(Li₇La₃Zr₂O₁₂) garnet powder is prepared by second calcinating thegrinded mixture for 10 to 30 hours in a temperature range of 1100 to1300° C.

The operation of preparing a mixture by first dry mixing is an operationof simply mixing raw material powders, and no energy is transferred tothe powders in the process. There may be a 5 minute rest time in eachstep to prevent the transfer of heat energy into the powders. The mixingmethod includes a dry method or a wet method. Dry mixing using aplanetary mill owned by the inventors may be carried out since, in thecase of wet mixing, the process time may increase, (such as by one dayor more to dry the mixture) and side reactions due to solvents mayoccur. As the mixing condition, the planetary milling condition ismilder, and the number of zirconia balls may be approximately half whencompared to the two-step dry mixing.

In the LLZ garnet powder, the molar ratio of the Li₂CO₃, La₂O₃, ZrO₂,and Al₂O₃ is 6.5 to 8.3 mol:3 mol:4 mol 0.02 to 1.075 mol.

In the LLZ garnet powder, some of the Li may be substituted with Al. Thesubstituted Al may be Al₂O₃ being doped in 0.1 to 5% by weight withrespect to the LLZ.

The operation of first calcinating the mixture may be carried out for 5to 7 hours in a temperature range of 800 to 1000° C. In this operation,CO₂ and H₂O residues present inside the mixture powder are removed.Particularly, when a carbonic acid component of the Li₂CO₃ is notremoved, the carbonic acid component remains inside the LLZ garnetpowder, and becomes a factor causing a decrease of density and ionicconductivity, therefore, CO₂ needs to be removed. Calcination may becarried out for 6 hours at 900° C.

In the operation of grinding the calcinated mixture to a powder size of1 to 4 μm through dry grinding, some of the calcinated mixture may befirmly aggregated, and some may experience a phase shift of the garnetstructure. Consequently, when performing the final calcination process,milling may be carried out under a mixing condition stronger than thefirst calcination step in order to simultaneously have the crushing ofthe aggregated powder and the powder mixing for maximizing the reaction,and the number of zirconia balls may be approximately twice compared tothe first calcination step.

In the operation of preparing cubic-phased LLZ (Li₇La₃Zr₂O₁₂) garnetpowder by second calcinating the grinded mixture for 10 to 30 hours in atemperature range of 1100 to 1300° C., the temperature and the time forproducing the LLZ garnet powder may be different depending on thecomposition of the raw materials. Particularly, in the case of the rawmaterials including hydroxide, the operation may be carried out in a lowtemperature range of 50 to 100° C.

The method for manufacturing the LLZ garnet powder may further includean operation of analyzing the LLZ garnet powder, and the analysis may becarried out using X-Ray Diffraction (XRD), Raman Spectroscopy, orInductively Coupled Plasma Mass Spectrometry (ICP-MS). The XRD mayidentify the LLZ phase and impurities, and through the Raman, phases andimpurities corresponding to regions having hundreds of micrometers orless, which are difficult to be determined with XRD, may be identified.In addition, using ICP, differences between target compositions andsynthesized compositions may be compared by identifying the ratio ofeach atom composition in the LLZ.

In addition, the present disclosure provides a solid electrolyte sheetincluding the LLZ (Li₇La₃Zr₂O₁₂) garnet powder. The solid electrolytesheet may have a pure cubic-phased crystal structure without includingimpurities, and have improved ionic conductivity as a solid electrolytesheet in a powder phase compared to existing solid electrolytes in apellet phase.

In addition, the present disclosure provides a method for manufacturinga solid electrolyte sheet using a hot press including preparing the LLZ(Li₇La₃Zr₂O₁₂) garnet powder; and manufacturing a solid electrolytesheet by hot pressing the garnet powder for 30 minutes to 2 hours in atemperature range of 1050 to 1250° C. under argon atmosphere.

In the operation of manufacturing a solid electrolyte sheet using a hotpress, when the temperature is lower than 1050° C., a tetragonal phasethat is produced advantageously at low temperature may be formed, andwhen the temperature is higher than 1250° C., an impurity phase such aspyrochlore (La₂Zr₂O₇) may be formed, or melting of the garnet powder mayoccur.

The solid electrolyte sheet may have a thickness of 0.01 to 5 mm.Specifically, when the thickness of the solid electrolyte sheet is lessthan 0.01 mm, cracks or fractures may occur due to the weak physicalproperties, and when greater than 5 mm, the energy density of a batterycell may greatly decrease due to the weight of the solid electrolyte.

In the solid electrolyte sheet, almost 100% of the powder used may bemanufactured to a sheet, and the solid electrolyte sheet has ionicconductivity ranging from 6×10⁻⁴ to 10×10⁻⁴ S/cm.

The method for manufacturing the solid electrolyte sheet may furtherinclude an operation of analyzing the solid electrolyte sheet, and theanalysis may be carried out using X-Ray Diffraction (XRD), RamanSpectroscopy, or Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

Consequently, the garnet powder according to the present disclosure maybe prepared as powder through a two-step calcination process. Therefore,the obtained content of the garnet powder is high compared to existinggarnet pellets including a very small amount of garnet powder, and theprepared garnet powder has a cubic-phased crystal structure with highcrystallizability.

In addition, the solid electrolyte sheet including the LLZ(Li₇La₃Zr₂O₁₂) garnet powder according to the present disclosure may usea hot press process. Therefore, a solid electrolyte sheet having a purecubic-phased crystal structure may be manufactured without includingimpurities, and the solid electrolyte sheet is effective in improvingionic conductivity compared to existing solid electrolytes.

EXAMPLES

Hereinafter, the present disclosure will be described in more detailwith reference to examples, however, the scope of the present disclosureis not limited to the following examples.

Manufacture of Garnet Powder Example 1

A mixture was prepared by first dry mixing Li₂CO₃, La₂O₃, ZrO₂ andAl₂O₃, which are raw materials, in a molar ratio of 7.7:3:4:0.5. Next,the mixture was first calcinated for 6 hours at 900° C., and then thepowder was ground to an average particle size of 1 to 4 μm. The groundmixture was second calcinated for 20 hours at 1200° C., and cubic-phasedLLZ (Li₇La₃Zr₂O₁₂) garnet powder was obtained.

Comparative Example 1

LLZ (Li₇La₃Zr₂O₁₂) garnet powder was obtained by grinding andcalcinating a mixture in the same manner as in Example 1 except that themixture was prepared by first dry mixing LiOH, La₂O₃, ZrO₂, and Al₂O₃,which are raw materials, in a molar ratio of 15.4:3:4:0.5.

Comparative Example 2

LLZ (Li₇La₃Zr₂O₁₂) garnet powder was obtained by grinding andcalcinating a mixture in the same manner as in Example 1 except that themixture was prepared by first dry mixing LiOH, La(OH)₃, ZrO₂, and Al₂O₃,which are raw materials, in a molar ratio of 15.4:6:4:0.5.

Comparative Example 3

LLZ (Li₇La₃Zr₂O₁₂) garnet powder was obtained by grinding andcalcinating a mixture in the same manner as in Example 1 except that themixture was prepared by first dry mixing Li₂CO₃, La(OH)₃, ZrO₂, andAl₂O₃, which are raw materials, in a molar ratio of 7.7:6:4:0.5.

Manufacture of Solid Electrolyte Sheet Example 2

A solid electrolyte sheet was manufactured by hot pressing thecubic-phased LLZ (Li₇La₃Zr₂O₁₂) garnet powder manufactured in Example 1for 1 hour at a temperature of 1100° C. under argon (Ar) atmosphere.Herein, the process was carried out under a pressure of 50 MPa, and thesolid electrolyte sheet was manufactured to a thickness of 5 mm and asize of 30×30 mm².

Comparative Example 4

A solid electrolyte sheet was manufactured in the same manner as inExample 2 except that the cubic-phased LLZ (Li₇La₃Zr₂O₁₂) garnet powdermanufactured in Example 1 was hot pressed for 1 hour at a temperature of900° C. under argon (Ar) atmosphere.

Comparative Example 5

A solid electrolyte sheet was manufactured in the same manner as inExample 2 except that the cubic-phased LLZ (Li₇La₃Zr₂O₁₂) garnet powdermanufactured in Example 1 was hot pressed for 1 hour at a temperature of1000° C. under argon (Ar) atmosphere.

Comparative Example 6

A solid electrolyte sheet was manufactured by preparing LLZ(Li₇La₃Zr₂O₁₂) garnet pellets using a general process, and thencalcinating the pellets again. In the solid electrolyte sheet, thegarnet pellets were prepared by being first calcinated for 6 hours at atemperature of 900° C. and then applying a pressure of 130 MPa thereto,and then the solid electrolyte sheet was manufactured by secondcalcinating the pellets again for 20 hours at a temperature of 1200° C.

Test Example 1: X-Ray Diffraction (XRD) Measurements of Garnet PowderManufactured in Example 1 and Comparative Examples 1 to 3

In order to identify the composition and the crystallizability of thegarnet powder manufactured in Example 1 and Comparative Examples 1 to 3,peaks were analyzed using an XRD device, and the results are shown inFIG. 1.

FIG. 1 shows the XRD measurement results of the garnet powdermanufactured in Example 1 and Comparative Examples 1 to 3. As identifiedin FIG. 1, impurities were observed in all the garnet powdermanufactured in Example 1 and Comparative Examples 1 to 3, however, itwas seen that the amount of the impurities is small in the examplesconsidering the small impurity peaks observed in the examples includingLa₂O₃, compared to Comparative Examples 2 and 3 including La(OH)₃ inwhich relatively large impurity peaks were observed.

Test Example 2: Raman Spectroscopy Measurements of Garnet PowderManufactured in Example 1 and Comparative Examples 1 to 3

In order to identify the crystal phase and the impurities of the garnetpowder manufactured in Example 1 and Comparative Examples 1 to 3, peakswere analyzed using a Raman Spectroscopy device, and the results areshown in FIGS. 2A to 2D.

FIG. 2A shows the Raman measurement result of the garnet powdermanufactured in Example 1, FIG. 2B shows the Raman measurement result ofthe garnet powder manufactured in Comparative Example 1, and FIG. 2Cshows the Raman measurement result of the garnet powder manufactured inComparative Example 2. In addition, FIG. 2D shows the Raman measurementresult of the garnet powder manufactured in Comparative Example 3.

As identified in FIGS. 2A to 2D, the appearance of impurity peaksinstead of the cubic garnet peaks was identified in Comparative Examples2 and 3 while only cubic garnet peaks were observed in ComparativeExample 1, and it was identified that, in Example 1, the formed graphwas from cubic garnet although a small amount of impurities wasobserved.

Test Example 3: Inductively Coupled Plasma Mass Spectrometry (ICP-MS)Measurements of Garnet Powder Manufactured in Example 1 and ComparativeExamples 1 to 3

In order to identify the lithium content (mol) of the garnet powdermanufactured in Example 1 and Comparative Examples 1 to 3, analysis wascarried out using an ICP-MS device, and the results are shown in FIGS. 3and 4.

FIG. 3 shows the ICP measurement results of the garnet powdermanufactured in Example 1 and Comparative Examples 1 to 3. It wasidentified that, in the garnet synthesis, an impurity phase was formedwhen Li is included in 6 mol or less, therefore, the example includingLa₂O₃ and Li₂CO₃ with 6 mol or higher of Li forming a stable garnetphase was advantageous in the garnet powder process.

FIG. 4 is an SEM picture of the garnet powder manufactured in Example 1.As shown in FIG. 4, the formation of the garnet powder having particlesizes of a few to tens of μm was identified.

In conclusion, based on the XRD, the Raman and the ICP analysis resultscarried out in Text Examples 1 to 3, it was demonstrated that the garnetpowder of Example 1 including La₂O₃ and Li₂CO₃ is advantageous.

Test Example 4: Density and Ionic Conductivity Measurements of GarnetPowder Manufactured in Example 2 and Comparative Examples 4 to 6

The density and the ionic conductivity of the garnet powder manufacturedin Example 2 and Comparative Examples 4 to 6 were measured, and theresults are shown in the following Table 1.

TABLE 1 Category Density (%) Ionic conductivity(S/cm) Example 2 98 8.7 ×10⁻⁴ Comparative Example 4 82 9.1 × 10⁻⁶ Comparative Example 5 93 7.3 ×10⁻⁵ Comparative Example 6 85   1 × 10⁻⁴

As shown in Table 1, it was identified that the garnet manufactured inExample 2 had significantly superior density and ionic conductivitycompared to the garnet manufactured in Comparative Examples 4 to 6.Particularly, the ionic conductivity in Example 2 carrying out the hotpress process at 1100° C. was superior to the ionic conductivity inComparative Examples 4 and 5 carrying out the hot press process attemperatures of 900° C. and 1000° C.

FIG. 5 is a graph showing the density and the ionic conductivity of thesolid electrolyte sheet manufactured in Example 2 and ComparativeExamples 4 and 5. As identified in FIG. 5, it was seen that generalrelative density when the pellet was prepared and then calcinated wasapproximately 85%, and the ionic conductivity was approximately 1×10⁻⁴S/cm. Meanwhile, in the hot press process using the garnet powder, thedensity increased as the process temperature increased, and the ionicconductivity also increased as well. Consequently, it was identifiedthat maximum ionic conductivity was obtained in Example 2 carrying outthe hot press process at a temperature of 1100° C. However, at processtemperatures of 1250° C. or higher, an impurity phase may be formed orsome of the garnet powder may be melted.

Test Example 5: X-Ray Diffraction (XRD) Measurements of Garnet PowderManufactured in Examples 1 and 2, and Comparative Examples 4 and 5

In order to identify the particle crystallizability and the presence ofimpurities of the garnet powder manufactured in Examples 1 and 2, andComparative Examples 4 and 5, peaks were analyzed using an XRD device,and the results are shown in FIG. 6.

FIG. 6 shows the XRD measurement results of the solid electrolyte sheetmanufactured in Examples 1 and 2, and Comparative Examples 4 and 5. Asidentified in FIG. 6, it was seen that the garnet powder manufactured inExample 1 had a cubic phase with a small amount of impurities present.Meanwhile, it was identified that the solid electrolyte sheetmanufactured in Comparative Examples 4 and 5 carrying out a hot presshad a cubic phase with low crystallizability, and the solid electrolytesheet manufactured in Example 2 had a pure cubic phase with highcrystallizability. Based on the above observation, it was identifiedthat the impurities present in the garnet powder manufactured in Example1 were removed through the hot press process.

Test Example 6: Raman Spectroscopy Measurements of Garnet PowderManufactured in Example 2, and Comparative Examples 4 and 5

In order to identify the crystal phase and the impurities of the garnetpowder manufactured in Example 2 and Comparative Examples 4 and 5, peakswere analyzed using a Raman Spectroscopy device, and the results areshown in FIGS. 7 and 8A-8C.

FIGS. 7A-7C show the Raman measurement results of the solid electrolytesheet manufactured in Example 2 and Comparative Examples 4 and 5. Asidentified in FIGS. 7A-7C, a tetragonal phase and a cubic phase weremixed in the solid electrolyte sheet manufactured in ComparativeExamples 4 and 5, and impurity peaks were observed. Meanwhile, onlycubic-phased peaks were observed in Example 2.

FIGS. 8A-8C are SEM pictures of the solid electrolyte sheet manufacturedin Example 2 and Comparative Examples 4 and 5. As identified in FIGS.8A-8C, it was seen that the size of the particles increased as thetemperature of the hot press process increased, and closed pores wereobserved in Example 2 carrying out the process at 1100° C., and this wasa phenomenon due to particle growth. Based on the above observation, itwas identified that grain boundary resistance decreased as the particlesizes of the material increased inducing the increase of ionicconductivity.

Consequently, it was identified that the content of the LLZ(Li₇La₃Zr₂O₁₂) garnet powder obtained according to the presentdisclosure is high, and the garnet powder has a cubic-phased crystalstructure with high crystallizability, and by using a hot press process,the solid electrolyte sheet using the garnet powder has a purecubic-phased crystal structure without impurities, and has improvedionic conductivity compared to existing solid electrolytes.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A method for manufacturing Li₇La₃Zr₂O₁₂ (LLZ)garnet powder comprising: preparing a mixture by first dry mixingLi₂CO₃, La₂O₃, ZrO₂, and Al₂O₃; first calcining the mixture for 5 to 7hours in a temperature range of 800 to 1000° C.; grinding the calcinatedmixture to a powder with an average particle size of 1 to 4 μm by drygrinding to form a ground mixture; and preparing a cubic-phased LLZgarnet powder by second calcining the ground mixture for 10 to 30 hoursin a temperature range of 1100 to 1300° C., wherein Al substitutes someof the Li of LLZ garnet powder, and is doped in the form of Al₂O₃ to theLLZ garnet powder.
 2. The method for manufacturing LLZ garnet powder ofclaim 1, wherein, in the LLZ garnet powder, a molar ratio of the Li₂CO₃,the La₂O₃, the ZrO₂, and the Al₂O₃ is 7:3:4:0.02 to 1.075.
 3. The methodfor manufacturing LLZ garnet powder of claim 1, wherein the substitutedAl is included in 0.02 to 1.075 mol, and Al is doped in the form ofAl₂O₃ at 0.1 to 5% by weight with respect to the LLZ garnet powder. 4.The method for manufacturing LLZ garnet powder of claim 1 furthercomprising analyzing the LLZ garnet powder, wherein the analysis iscarried out using X-Ray Diffraction (XRD), Raman Spectroscopy, orInductively Coupled Plasma Mass Spectrometry (ICP-MS).